You have reported a bad site on Google Webmaster Tools SPAM report.
Assuming you are sure it was a bad site, did you see Google punishing it or doing something after your report?
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I did once, for a site which had lots of hidden links.
I received no acknowledgment, but within 7 days the offending site disappeared from the front page of results (I didn't check how far down they slipped, they may well have disappeared altogether) they re-appeared 6-7 weeks later, slightly further down the first page with the hidden links removed.